Field of the Invention
The present invention relates to an image formation apparatus and an image formation method which use inks varying in transmittance.
Description of the Related Art
There are various recording methods for recording apparatuses configured to record images on sheet-like recording media such as a paper sheet and a film. An inkjet recording method is known as one of the recording methods. In recent years, various recording agents have been proposed for a recording apparatus employing the inkjet recording method. A pigment ink is a typical example of the recording agents.
As for the pigment ink, a color material exists as particles with a size of about several tens of nanometers in the recording agent. Having a large particle size of the color material, the pigment ink hardly permeates into the recording medium and is fixed on a surface of the recording medium. In the case of pigment inks, a color material printed first is fixed on the surface of the recording medium, and a color material printed after a while is fixed on the first-printed color material. As described above, which one of an upper layer or a lower layer a pigment ink is arranged in tends to be determined depending on the order of fixation.
Occurrence of two specular reflection coloring phenomena is known as characteristics of pigment inks. Specifically, bronzing and a thin-film interference phenomenon are known to occur.
The bronzing is a phenomenon in which, for example, specular reflection assumes magenta in a region where a cyan ink is widely used as the color material arranged in the upper layer. The bronzing occurs due to wavelength dependence of an index of refraction by the pigment ink arranged in the upper layer on the recording medium, and is caused by the pigment ink color material itself.
The thin-film interference phenomenon is an optical thin-film interference phenomenon occurring in a case where a pigment ink with high transmittance (for example, a transparent ink) is fixed in the upper layer with a thickness of 2 μm or less. In the optical thin-film interference phenomenon, chroma and hue in the coloring of the specular reflection vary depending on the thickness. It is known that, in the thin-film interference phenomenon, the coloring can be reduced (turned into white color) by increasing the thickness of the ink (setting the thickness to 2 μm or more) or by making the thickness of the ink uneven (increasing the variation of the thickness).
Japanese Patent Laid-Open No. 2012-90105 proposes a technique of reducing the aforementioned two specular reflection coloring phenomena (bronzing and thin-film interference phenomenon). In Japanese Patent Laid-Open No. 2012-90105, the specular reflection coloring due to the bronzing can be reduced by forming the upper layer of an image with an ink with high transmittance (transparent color material) whose index of refraction has small wavelength dependence. Furthermore, a color material amount of the ink with high transmittance (transparent color material) in a target pixel and a color material amount of the ink with high transmittance (transparent color material) in each of pixels around the target pixel are controlled to be different from each other, and the thickness is thereby made uneven to locally generate lights of various colors. In a case where the local lights of various colors are viewed macroscopically, the various colors are blended and the thin-film interference phenomenon is observed such that the observed light is close to a white light. As a result, the specular reflection coloring due to the thin-film interference phenomenon is reduced.
However, in the method described in aforementioned Japanese Patent Laid-Open No. 2012-90105, the thickness of the ink with high transmittance (transparent color material) arranged in the upper layer of the image is made uneven, and roughness on the image surface is increased. Accordingly, gloss uniformity (particularly, gloss clarity and gloss clarity) decreases.